One of the principal mechanisms by which cellular regulation is effected is through the transduction of extracellular signals into intracellular signals that in turn modulate biochemical pathways. Examples of such extracellular signaling molecules include growth factors, cytokines, and chemokines. The cell surface receptors of these molecules and their associated signal transduction pathways are therefore one of the principal means by which cellular behavior is regulated. Because cellular phenotypes are largely influenced by the activity of these pathways, it is currently believed that a number of disease states and/or disorders are a result of either aberrant activation or functional mutations in the molecular components of signal tranduction pathways. Consequently, considerable attention has been devoted to the characterization of these proteins.
For example, the polypeptide cytokine tumor necrosis factor (TNF) is normally produced during infection, injury, or invasion and serves as a pivotal mediator of the inflammatory response. In recent years, a number of in vivo animal and human studies have demonstrated that overexpression of TNF by the host in response to disease and infection is itself responsible for the pathological consequences associated with the underlying disease. For example, septic shock as a result of massive bacterial infection has been attributed to infection-induced expression of TNF. Thus, systemic exposure to TNF at levels comparable to those following massive bacterial infection has been shown to result in a spectrum of symptoms (shock, tissue injury, capillary leakage, hypoxia, pulmonary edema, multiple organ failure, and high mortality rate) that is virtually indistinguishable from septic shock syndrome (Tracey and Cerami, Ann. Rev. Med., 1994, 45, 491-503). Further evidence has been provided in animal models of septic shock, in which it has been demonstrated that systemic exposure to anti-TNF neutralizing antibodies block bacterial-induced sepsis (Tracey and Cerami, Ann. Rev. Med., 1994, 45, 491-503). In addition to these acute effects, chronic exposure to low-dose TNF results in a syndrome of cachexia marked by anorexia, weight loss, dehydration, and depletion of whole-body protein and lipid. Chronic production of TNF has been implicated in a number of diseases including AIDS and cancer (Tracey and Cerami, Ann. Rev. Med., 1994, 45, 491-503).
Studies examining the molecular events associated with TNF exposure have revealed that activation of the transcription factor NF-kappa-B is a critical component of many of the effects attributed to TNF (Tewari and Dixit, Curr. Opin. Genet. Dev., 1996, 6, 39-44). More recently, the intracellular protein TRADD has been identified as a critical link between TNF receptor binding and downstream activation of NF-kappa-B. Thus, overexpression of native TRADD was shown to activate NF-kappa-B in the absence of TNF and dominant negative mutants of TRADD block TNF-induced NF-kappa-B activation (Tewari and Dixit, Curr. Opin. Genet. Dev., 1996, 6, 39-44). A second effect of TNF in many cell types is the induction of apoptosis, or programmed cell death. As with NF-kappa-B activation, TRADD overexpression has been shown to mimic TNF induction of apoptosis as well (Darnay and Aggarwal, J. Leukoc. Biol., 1997, 61, 559-566; Tewari and Dixit, Curr. Opin. Genet. Dev., 1996, 6, 39-44).
As a result of these advances in the understanding of TNF overexpression in certain disease states, there is a great desire to provide compositions of matter which can inhibit the cellular effects elicited by TNF. In vitro studies have shown that maximal cellular responses to TNF are elicited when as little as 10% of TNF cell membrane receptors are occupied (Tracey and Cerami, Ann. Rev. Med., 1994, 45, 491-503). These data indicate that downstream effectors proteins such as TRADD are the rate-limiting step of TNF action and would therefore serve as the most efficient targets for inhibition of TNF-induced events.
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of TRADD. Antisense oligonucleotides capable of inhibiting TRADD function may therefore prove to be uniquely useful in a number of therapeutic, diagnostic and research applications.